An exhaust gas sensor may be positioned in an exhaust system of a vehicle to detect an air/fuel ratio of exhaust gas exhausted from an internal combustion engine of the vehicle. The exhaust gas sensor readings may be used to control operation of the internal combustion engine to propel the vehicle.
Degradation of an exhaust gas sensor may cause engine control degradation that may result in increased emissions and/or reduced vehicle drivability. Accordingly, accurate determination of exhaust gas sensor degradation may reduce the likelihood of engine control based on readings from a degraded exhaust gas sensor. In particular, an exhaust gas sensor may exhibit six discrete types of degradation behavior. The degradation behavior types may be categorized as asymmetric type degradation (e.g., rich-to-lean asymmetric delay, lean-to-rich asymmetric delay, rich-to-lean asymmetric filter, lean-to-rich asymmetric filter) that affects only lean-to-rich or rich-to-lean exhaust gas sensor response rates, or symmetric type degradation (e.g., symmetric delay, symmetric filter) that affects both lean-to-rich and rich-to-lean exhaust gas sensor response rates. The delay type degradation behaviors may be associated with the initial reaction of the exhaust gas sensor to a change in exhaust gas composition and the filter type degradation behaviors may be associated with a duration after an initial exhaust gas sensor response to transition from a rich-to-lean or lean-to-rich exhaust gas sensor output.
Previous approaches to monitoring exhaust gas sensor degradation, particularly identifying one or more of the six degradation behaviors, have relied on intrusive data collection. That is, an engine may be purposely operated with one or more rich to lean or lean to rich transitions to monitor exhaust gas sensor response. However, these excursions may be restricted to particular operating conditions that do not occur frequently enough to accurately monitor the sensor. Further, these excursions may increase engine operation at non-desired air/fuel ratios that result in increased fuel consumption and/or increased emissions. Additionally, large amounts of background noise present in the collected samples may confound accurate determination of the sensor degradation.
As described in U.S. patent application Ser. No. 13/410,171, filed on Mar. 1, 2012, the entire contents of which are incorporated herein by reference for all purposes, the inventors herein have recognized the above issues and identified a non-intrusive approach that utilizes a robust parameter for determining exhaust gas sensor degradation. In one embodiment, a method of monitoring an exhaust gas sensor coupled in an engine exhaust comprises indicating exhaust gas sensor degradation, including asymmetric degradation, based on a time delay and line length of each sample of a set of exhaust gas sensor responses collected during a commanded change in air-fuel ratio.
The exhaust gas sensor time delay and line length may provide a robust signal that has less noise and higher fidelity than previous approaches. In doing so, the accuracy of the sensor degradation determination may be improved. In one example, the commanded change in lambda may be entry into or exit out of deceleration fuel shut-off (DFSO). During entry into DFSO, the engine may be commanded from stoichiometric operation to lean operation, and during exit out of DFSO, the engine may be commanded from lean operation to stoichiometric operation. As such, the exhaust gas sensor time delay and line length may be monitored during conditions that approximate lean-to-rich and rich-to-lean transitions to determine if any of the six discrete sensor degradation behaviors are present without intrusive excursions.
By determining degradation of an exhaust gas sensor using a non-intrusive approach with data collected during DFSO, exhaust gas sensor degradation monitoring may be performed in a simple manner. Further, by using the exhaust gas sensor output to determine which of the degradation behaviors the sensor exhibits, closed loop feedback control may be improved by tailoring engine control (e.g., fuel injection amount and/or timing) responsive to indication of the particular degradation behavior of the exhaust gas sensor to reduce the impact on vehicle drivability and/or emissions due to exhaust gas sensor degradation.
The inventors herein have also recognized that, in such approaches which indicate sensor degradation based on comparing measured time delays and line lengths to expected responses, the expected response may be difficult to predict. For example, changes in air mass, purge flow, and similar noises may contribute to inaccuracies in expected response determination and may result in reduced accuracy in sensor fault estimations.
In one example approach, in order to address these issues, a method of monitoring an upstream exhaust gas sensor coupled in an engine exhaust is provided. The method comprises indicating exhaust gas sensor degradation based on a downstream exhaust gas sensor responding before the upstream exhaust gas sensor during a commanded change in air-fuel ratio.
In this way, sensor degradation may be at least partially based on comparing the response of the upstream sensor with the downstream sensor so that sensor faults may be identified even during conditions where an expected sensor response determination is inaccurate, e.g., due to changes in air mass, purge flow, and similar noises. Further, the downstream sensor response may be used to adapt and refine an expected response for the upstream sensor so that sensor degradation may be indicated based on comparing measured time delays and line lengths to expected responses.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.